1. Field of the Invention
The present invention relates to a hydraulic system for controlling a brake system and a suspension system of a heavy equipment for construction capable of travelling, such as a wheel-type excavator, and more particularly to a hydraulic system, by which a brake system and a suspension system of a wheel-type excavator can be operated independently or systematically by operating a single operating means.
2. Prior Arts
In a wheel-type excavator which is one of heavy equipments for construction, a suspension system is a system to perform a buffering function in the course of the travelling of the excavator and to maintain the balance of the excavator while the excavator is operated at an inclined area. Meanwhile, a brake system of a wheel-type excavator has a travel-brake system for braking the excavator having been travelling, a park-brake system for preventing the excavator from falling down when it is parked, and a work-brake system for preventing the excavator from being pushed or pulled by an excavator force thereof in the course of excavating to thereby retain the excavator in a position in a stable manner so as to enable the excavator to perform a stable excavating operation.
FIG. 1 shows a systematic diagram of a brake system and a suspension system of a conventional wheel-type excavator, which include a plurality of hydraulic pumps 2a and 2b driven by a single engine 1, a travel-brake cylinder 7, a park-brake cylinder 13 and a suspension system locking cylinder 16, driven by hydraulic pumps 2a and 2b. A brake cut-off valve 3, a pressure accumulator 4, a travel-brake valve 5, and a pilot check valve 6 are provided in a first oil path 31 interconnecting hydraulic pump 2a and travel-brake cylinder 7, while oil path switching solenoid valves 10 and 12 are respectively disposed between hydraulic pump 2b and park-brake cylinder 13 and between hydraulic pump 2b and suspension system locking cylinder 16 in a second oil path 32. Further, a relief valve 14 is disposed in second oil path 32 so that a predetermined pressure is built up in second oil path 32.
In the meantime, a pedal or a lever 33 handled by an operator is provided at travel-brake valve 5 for operating the travel-brake system, and electric switches 9 and 11 for receiving driving power therethrough from battery 8a and 8b are respectively provided at each of oil path switching solenoid valves 10 and 12 for operating the suspension system and the park-brake system.
In the conventional brake system and suspension system of excavator constructed as described above, when the excavator travels normally, two electric switches 9 and 11 are switched on to make two oil path switching solenoid valves 10 and 12 be switched. In this case, a working oil exhausted from hydraulic pump 2b builds up a pressure in second oil path 32 by relief valve 14, and a suspension system control valve 15 is switched by solenoid valve 10 to make the working oil in suspension system locking cylinder 16 be in an opened-circuit-state so that the suspension system can perform a suspension function.
Further, the pressure is applied through solenoid valve 12 to park-brake cylinder 13 to make the park-brake system be released, and through a pilot line 34 to pilot check valve 6 in first oil path 31 to rid pilot check valve 6 of its direction control function, so that travel-brake cylinder 7 can be operated by travel-brake valve 5 and accordingly the travel-brake system can be operated.
To change a travelling state of the system as described above to a working state thereof, two electric switches 9 and 11 are switched off to make the driving power from batteries 8a and 8b be cut off. When electric switch 11 is off, solenoid valve 12 is switched as shown in FIG. 1 to cut off second oil path 32, and thereby the working oil exhausted from hydraulic pump 2b is returned through second oil path 32 and relief valve 14 disposed in second oil path 32 to a tank T. Further, a pressure having built up in pilot line 34 is removed, and accordingly pilot check valve 6 is restored to have its direction controlling valve. In this state, travel-brake valve 5 is operated by one time, then the working oil exhausted from hydraulic pump 2a is stored in pressure accumulator 4 through brake cut-off valve 3 and then is flowed into the brake system through travel-brake valve 5, so that pressure is continuously built up between pilot check valve 6 and travel-brake cylinder 7 and thereby the park-brake system and the travel-brake system is operated continuously.
Meanwhile, when electric switch 9 is off, suspension system controlling valve 15 is switched as shown in FIG. 1, and accordingly the suspension system is locked. In the brake system and suspension system of the conventional wheel-type excavator, for switching the systems, a lot of switches, and a pedal or a lever must be separately operated, and accordingly there has been a significant inconvenience in handling the system and a possibility of danger to mishandle the switches and the lever.
That is, because the operator must confirm the operation state of the respective sections of the system one by one in detail, the working efficiency is largely lowered. Even in case of mishandling the switches, a fatal damage can be effected on the brake system. As an example, when the excavator is driven to travel in a state that electric switch 11 is on, which is a mishandling accident frequently happened, the park-brake system is broken down.